1. Field of the Invention
This invention relates generally to a powertrain for a vehicle, and, more particularly, to a powertrain having multiple power sources including an electric motor for driving a set of vehicle wheels.
2. Description of the Prior Art
Hybrid electric powertrains have been developed that include an electric motor and an internal combustion (IC) engine that can operate independently or in combination depending on the driving conditions, the state of charge of a traction battery, and the power source that most efficiently meets the current power demands imposed by the vehicle operator.
Most electric hybrid vehicles available commercially are front wheel drive vehicles, in which only the front wheels are driven. Hybrid electric powertrains, being developed for use in four-wheel drive vehicles, allow both the motor and engine to transmit power to a rear set of driven wheels.
When packaging an electric motor drive unit for a rear axle it is preferable to place the motor drive unit on the rear axle centerline for best packaging efficiency. The engine is located at the front to the vehicle in the engine compartment. Such electric hybrid drive systems, however, present packaging difficulties to the vehicle designer, particularly when layshaft gearing is used to transmit power from a longitudinal drive shaft to a rear axle. A ring and pinion mechanical drive, similar to an axle drive, will operate without layshaft gearing.
A need exists for a low-cost, hybrid electric powertrain in which one axle is driven by an electric motor or an IC engine in combination with the motor. To minimize cost, an electric machine would provide all hybrid functions including electric energy generation, electric vehicle launch, engine starting, electric boosting of engine power, and regenerative braking.